sparc/vdso/vdso2c.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * vdso2c - A vdso image preparation tool
0004  * Copyright (c) 2014 Andy Lutomirski and others
0005  *
0006  * vdso2c requires stripped and unstripped input.  It would be trivial
0007  * to fully strip the input in here, but, for reasons described below,
0008  * we need to write a section table.  Doing this is more or less
0009  * equivalent to dropping all non-allocatable sections, but it's
0010  * easier to let objcopy handle that instead of doing it ourselves.
0011  * If we ever need to do something fancier than what objcopy provides,
0012  * it would be straightforward to add here.
0013  *
0014  * We keep a section table for a few reasons:
0015  *
0016  * Binutils has issues debugging the vDSO: it reads the section table to
0017  * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
0018  * would break build-id if we removed the section table.  Binutils
0019  * also requires that shstrndx != 0.  See:
0020  * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
0021  *
0022  * elfutils might not look for PT_NOTE if there is a section table at
0023  * all.  I don't know whether this matters for any practical purpose.
0024  *
0025  * For simplicity, rather than hacking up a partial section table, we
0026  * just write a mostly complete one.  We omit non-dynamic symbols,
0027  * though, since they're rather large.
0028  *
0029  * Once binutils gets fixed, we might be able to drop this for all but
0030  * the 64-bit vdso, since build-id only works in kernel RPMs, and
0031  * systems that update to new enough kernel RPMs will likely update
0032  * binutils in sync.  build-id has never worked for home-built kernel
0033  * RPMs without manual symlinking, and I suspect that no one ever does
0034  * that.
0035  */
0036
0037 /*
0038  * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
0039  */
0040
0041 #include <inttypes.h>
0042 #include <stdint.h>
0043 #include <unistd.h>
0044 #include <stdarg.h>
0045 #include <stdlib.h>
0046 #include <stdio.h>
0047 #include <string.h>
0048 #include <fcntl.h>
0049 #include <err.h>
0050
0051 #include <sys/mman.h>
0052 #include <sys/types.h>
0053 #include <tools/be_byteshift.h>
0054
0055 #include <linux/elf.h>
0056 #include <linux/types.h>
0057 #include <linux/kernel.h>
0058
0059 const char *outfilename;
0060
0061 /* Symbols that we need in vdso2c. */
0062 enum {
0063     sym_vvar_start,
0064     sym_VDSO_FAKE_SECTION_TABLE_START,
0065     sym_VDSO_FAKE_SECTION_TABLE_END,
0066 };
0067
0068 struct vdso_sym {
0069     const char *name;
0070     int export;
0071 };
0072
0073 struct vdso_sym required_syms[] = {
0074     [sym_vvar_start] = {"vvar_start", 1},
0075     [sym_VDSO_FAKE_SECTION_TABLE_START] = {
0076         "VDSO_FAKE_SECTION_TABLE_START", 0
0077     },
0078     [sym_VDSO_FAKE_SECTION_TABLE_END] = {
0079         "VDSO_FAKE_SECTION_TABLE_END", 0
0080     },
0081 };
0082
0083 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
0084 static void fail(const char *format, ...)
0085 {
0086     va_list ap;
0087
0088     va_start(ap, format);
0089     fprintf(stderr, "Error: ");
0090     vfprintf(stderr, format, ap);
0091     if (outfilename)
0092         unlink(outfilename);
0093     exit(1);
0094     va_end(ap);
0095 }
0096
0097 /*
0098  * Evil macros for big-endian reads and writes
0099  */
0100 #define GBE(x, bits, ifnot)                     \
0101     __builtin_choose_expr(                      \
0102         (sizeof(*(x)) == bits/8),               \
0103         (__typeof__(*(x)))get_unaligned_be##bits(x), ifnot)
0104
0105 #define LAST_GBE(x)                         \
0106     __builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0))
0107
0108 #define GET_BE(x)                           \
0109     GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x))))
0110
0111 #define PBE(x, val, bits, ifnot)                    \
0112     __builtin_choose_expr(                      \
0113         (sizeof(*(x)) == bits/8),               \
0114         put_unaligned_be##bits((val), (x)), ifnot)
0115
0116 #define LAST_PBE(x, val)                        \
0117     __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0))
0118
0119 #define PUT_BE(x, val)                  \
0120     PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val))))
0121
0122 #define NSYMS ARRAY_SIZE(required_syms)
0123
0124 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
0125 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
0126 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
0127
0128 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
0129
0130 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
0131 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
0132 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
0133
0134 #define ELF_BITS 64
0135 #include "vdso2c.h"
0136 #undef ELF_BITS
0137
0138 #define ELF_BITS 32
0139 #include "vdso2c.h"
0140 #undef ELF_BITS
0141
0142 static void go(void *raw_addr, size_t raw_len,
0143            void *stripped_addr, size_t stripped_len,
0144            FILE *outfile, const char *name)
0145 {
0146     Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
0147
0148     if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
0149         go64(raw_addr, raw_len, stripped_addr, stripped_len,
0150              outfile, name);
0151     } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
0152         go32(raw_addr, raw_len, stripped_addr, stripped_len,
0153              outfile, name);
0154     } else {
0155         fail("unknown ELF class\n");
0156     }
0157 }
0158
0159 static void map_input(const char *name, void **addr, size_t *len, int prot)
0160 {
0161     off_t tmp_len;
0162
0163     int fd = open(name, O_RDONLY);
0164
0165     if (fd == -1)
0166         err(1, "%s", name);
0167
0168     tmp_len = lseek(fd, 0, SEEK_END);
0169     if (tmp_len == (off_t)-1)
0170         err(1, "lseek");
0171     *len = (size_t)tmp_len;
0172
0173     *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
0174     if (*addr == MAP_FAILED)
0175         err(1, "mmap");
0176
0177     close(fd);
0178 }
0179
0180 int main(int argc, char **argv)
0181 {
0182     size_t raw_len, stripped_len;
0183     void *raw_addr, *stripped_addr;
0184     FILE *outfile;
0185     char *name, *tmp;
0186     int namelen;
0187
0188     if (argc != 4) {
0189         printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
0190         return 1;
0191     }
0192
0193     /*
0194      * Figure out the struct name.  If we're writing to a .so file,
0195      * generate raw output insted.
0196      */
0197     name = strdup(argv[3]);
0198     namelen = strlen(name);
0199     if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
0200         name = NULL;
0201     } else {
0202         tmp = strrchr(name, '/');
0203         if (tmp)
0204             name = tmp + 1;
0205         tmp = strchr(name, '.');
0206         if (tmp)
0207             *tmp = '\0';
0208         for (tmp = name; *tmp; tmp++)
0209             if (*tmp == '-')
0210                 *tmp = '_';
0211     }
0212
0213     map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
0214     map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
0215
0216     outfilename = argv[3];
0217     outfile = fopen(outfilename, "w");
0218     if (!outfile)
0219         err(1, "%s", argv[2]);
0220
0221     go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
0222
0223     munmap(raw_addr, raw_len);
0224     munmap(stripped_addr, stripped_len);
0225     fclose(outfile);
0226
0227     return 0;
0228 }